Mixing faucet base



FIG. 1 is a perspective view of mixing faucet base showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof, the right side is identical;

FIG. 5 is top view thereof, and;

FIG. 6 is a bottom view thereof. 

The ornamental design for "mixing faucet base", as shown and described. 